U.S. Pat. No. 6,829,477, entitled “Private Multiplexing Cellular Network” (also referred to here as the “'477 patent”), describes a private cellular system that provides cellular wireless service within an enterprise in conjunction with a public land mobile network (PLMN) (which is also referred to here as the “host” PLMN). The private cellular system uses licensed radio frequency spectrum that is allocated to the PLMN to provide the cellular wireless service within the enterprise.
The private cellular network described in the '477 patent includes a multiplexing function that is configured to support private subscribers and hybrid subscribers, as well as regular “public” subscribers. As used here, a “private” subscriber is a subscriber who is a subscriber of only the private cellular network and is only able to make calls to and receive calls from other private subscribers and hybrid subscribers. Each private subscriber has an assigned “private” MSISDN that is recognized only by the private cellular network and can only be called by other private subscribers and hybrid subscribers. Cellular service that is provided by the private cellular network using private MSISDNs is also referred to here as “private cellular service”. Also, private subscribers are not able to roam onto any public land mobile network.
As used here, a “public” subscriber is a “normal” subscriber of a public land mobile network—either the public land mobile network associated with the private cellular network or another public land mobile network. A public subscriber is able to use the private cellular network to make and receive calls to regular “public” MSISDN numbers that are assigned by public land mobile networks. Cellular service that is provided by the private cellular network using public MSISDNs is also referred to here as “public cellular service”. Also, each public subscriber is able to roam onto any public land mobile network with which the public subscriber's home PLMN has a roaming agreement.
As used here, a “hybrid” subscriber is a subscriber who is able to make calls to and receive calls from public subscribers, private subscribers, and other hybrid subscribers. Each hybrid subscriber has an assigned private MSISDN that other private subscribers and hybrid subscribers can use to call the hybrid subscriber using the private cellular network. Each hybrid subscriber also has a public MSISDN that public subscribers and other hybrid subscribers can use to call the hybrid subscriber regardless of what network the hybrid subscriber is using at the time any such call is made.
The multiplexer functionality described in the '477 patent implements GSM A-interface multiplexing to seamlessly provide private cellular service in connection with the private MSISDN numbers assigned to private and hybrid subscribers while also providing public cellular service to public subscribers (including both roamers and home subscribers of the host PLMN). Signaling and bearer traffic related to the provision of public cellular service is routed to switching functionality (for example, mobile switching center (MSC) functionality) included in the host PLMN. Such signaling and bearer traffic is routed to the host PLMN over the standard BSS/MSC interface. In other words, the private cellular network appears from the perspective of the host PLMN to be another BSS of the host PLMN. Signaling and bearer traffic related to the provision of private cellular service is routed to private switching functionality included in the private cellular network over the standard BSS/MSC interface. In the case of a GSM cellular network, the BSS/MSC interface is referred to as the “A Interface” and the multiplexer function is also referred to here as the “Private A-Link Intelligent Multiplexer” or “PALIM”.
In the private cellular network described in the '477 patent, subscription data for public subscribers is not maintained within the private cellular network since the private cellular network functions, from the perspective of the host PLMN, as a BSS and all subscription data is maintained within the host PLMN. However, the private cellular network needs to obtain and store subscription data for private and hybrid subscribers. Typically, the operator of the private cellular network provides the subscriber identity module (SIM) cards for private subscribers and, therefore, has easy access to the subscription data for private subscribers. However, the operator of the private cellular network typically does not supply the SIM cards for hybrid subscribers, which are typically provided by the subscriber's home PLMN. The subscriber information for hybrid users typically must be obtained from the hybrid users' SIM cards and manually entered into the private cellular network. As a result, the registration process for hybrid users has typically been inconvenient.
Also, as noted above, the PALIM functionality described in the '477 patent is configured to make the private cellular network appear as a single BSS to the host public land mobile network. As a result, only a single base station controller (BSC) is typically used in private cellular networks that employ PALIM functionality. However, in some private cellular network applications, it is desirable to use multiple base station controllers within a single private cellular network. For example, multiple base station controllers may be needed to handle the number of base transceiver stations (BTSs) that are deployed within the private cellular network and/or to handle different types of base transceiver stations (BTSs) that are deployed within the private cellular network.